1. Field of Technology
The present disclosure relates to nickel-base alloys and articles fabricated from and including such alloys. More particularly, the present disclosure relates to nickel-base alloys having high strength and substantial resistance to wear, oxidation, and thermal cracking in certain high-stress elevated temperature environments.
2. Description of the Background of the Technology
The manufacture of seamless steel tube and pipe using piercer points, pipe plugs, and reeler plugs is well known. A generally cylindrical steel bar or billet is heated to a temperature in the range of about 2000° F. to about 2300° F. (about 1093° C. to about 1260° C.) and then processed on a specialized hot forming apparatus such as, for example, a Mannesmann piercing mill. The apparatus typically includes: a pair of generally barrel-shaped, tapered upper and lower rolls disposed in skewed relation to one other; a set of opposed guide shoes disposed on opposite sides of central axes of the tapered rolls; and a generally spearhead-shaped plug, commonly referred to as a “piercer point”, mounted on the end of a mandrel and positioned intermediate and in front of the gorge of the barrel-shaped rolls. The rolls are driven to rotate. As the hot cylindrical-shaped billet is brought into contact with the rotating rolls, the billet spins and axially advances over the piercer point. As the piercer point pierces the billet axially, the billet material flows around the piercer point, and a hollow tube or shell results. The guide shoes are arranged 90 degrees circumferentially of each of the barrel-shaped rolls, and in an opposed relation to one another. As the shell is produced, it slidingly contacts the opposed guide shoes, which control the outer shape and thickness of the shell wall. The hollow shell is then typically reworked in a high mill or other elongator, such as a mandrel mill, Transval mill, or Assel mill, by rolling or drawing over a stationary mandrel, known as a “hi mill plug”, to provide a tube or pipe having the desired wall thickness and outer diameter.
A piercer point is subjected to very high stresses and temperatures during the piercing operation. After each piercing run, the piercer point is typically rapidly cooled by passing a stream of air or mist over the piercer point, or by quenching the piercer point in water. In certain seamless pipe manufacturing apparatus, the piercer point is internally cooled during the piercing operation, such as by circulating water within the piercer point. The purpose of reducing the temperature of the piercer point is to better maintain its physical integrity during successive piercing runs. However, the combination of the piercing conditions and the associated cooling practice subjects the piercer point to very high compressive and torsional stresses under conditions of extreme thermal shock, impact, and wear. Thus, the piercer point rather quickly wears and must be replaced regularly, which necessitates additional costs and apparatus downtime. Improving the resistance of piercer points to the extreme conditions to which they are subjected would increase the service life of the parts, improve throughput on the forming apparatus, and thereby reduce per unit cost of the fabricated seamless products.
Piercer points fabricated from several conventional alloys are prone to significant and unacceptable distortion (loss of original shape) caused by deformation and/or wear during the piercing operation. These conventional alloys also are prone to develop significant thermal fatigue cracking during piercing and/or cool down. Thermal cracking can lead to fragmentation and loss of material from the piercer point, which can result in the need for frequent piercer point replacement and unsatisfactory inner diameter surface quality in the seamless product.
Table 1 lists several conventional alloy compositions from which piercer points have been fabricated. In Table 1, and throughout the present disclosure, alloy compositions are provided as weight percentages based on total alloy weight. Alloy A, which is sometimes referred to in the trade as “Coloy”, is a high-cobalt alloy including significant levels of nickel and chromium. Alloy B, commonly designated as “Hastelloy C modified”, is a nickel-base alloy principally including molybdenum and chromium as alloying additions. Alloy C, which is known as “Inco NX-188”, also is a nickel-base alloy, including molybdenum and aluminum. The compositions of Alloys D and E, commonly referred to as “E-1” and “E-15”, respectively, are essentially low-carbon, low-alloy steels, and are typically used in less demanding piercing applications. In addition to what is listed in Table 1, Alloy E also includes 1.00 to 1.25 copper. The elements included in Table 1 and other tables herein without reported levels may be present in the alloys only in residual amounts.
TABLE 1Conventional Alloy Compositions for Piercer PointsAlloyNiCoCrMoWFeMnSiAlCA10.0-12.0Bal.18.0-22.01.013.0-17.08.02.00.70—0.12max.max.max.max.max.BBal.—14.0-18.015.0-19.03.0-5.05.00.50.5—0.02max.max.max.max.CBal.——16.0-20.0————7.0-9.00.1max.D2.00-2.20—1.20-1.50——Bal.0.55-0.700.20—0.20-0.30max.E0.50-0.901.20-1.301.50-1.750.08-0.13—Bal.0.500.50—0.15-0.25max.max.
Each of the alloys listed in Table 1 is deficient in that that it exhibits excessive wear and/or excessive cracking after a period of use under piercing conditions. Thus, piercer points fabricated from the alloys in Table 1 can only be used for a limited number of piercing runs before the point is unsuitable for further use and must be replaced. The limited service life of points made of the alloys in Table 1 is particularly evident when piercing relatively long billets, in which case a point is subjected to relatively high temperatures and for a relatively long time period.
The guide shoes of seamless tube fabricating apparatus are repeatedly rapidly heated to elevated temperature, and then rapidly cooled as the piercer point is quenched. Also, the guide shoes are contacted by the advancing spinning shell under an extreme stress load. Guide shoes are conventionally fabricated from certain iron-base and nickel-base alloys, including the conventional alloys listed in Table 2 below. The alloys in Table 2, identified in the table as F through H, are commonly referred to in the trade as “32-35”, “E-14”, and “CS-90” alloys, respectively.
TABLE 2Conventional Alloy Compositions for Seamless Mill Guide ShoesAlloyNiCrMoWFeMnSiCF34.0-36.031.0-33.00.510.0Bal.0.601.000.10-1.00max.max.max.max.G11.0-13.024.0-26.0——Bal.0.40-0.601.000.70-0.90max.H4.50-5.5019.0-21.0——Bal.0.600.30-0.700.90-1.10max.
Guide shoes cast from the alloys listed in Table 2 cannot withstand the thermal shock that results as the shoes are, over extended periods, subjected to repeated cycles of heating and cooling during piercing runs. As a result of this cyclic heating and cooling, thermal cracks can form on the surface of the guide shoes, and the shoes may fail. Also, certain of the conventional alloys from which guide shoes are fabricated, including the alloys listed in Table 2, have insufficient wear resistance and must be replaced often, necessitating additional cost and mill downtime.
Accordingly, it would be advantageous to provide alloys exhibiting improved performance and long service life when cast into piercer points and other seamless mill and hot working tools including, but not limited to, piercing mill guide shoes, rotary expander guide shoes, reeler guide shoes, and high-mill plugs. More generally, it would be advantageous to provide alloys exhibiting high strength at elevated temperatures and advantageous resistance to wear, oxidation, and thermal cracking in certain high-stress elevated temperature environments such as, for example, when applied in piercer points, guide shoes, and other mill tools used in the fabrication of seamless tubular products.